Optical disk apparatus with approximate focus control of laser beam

ABSTRACT

An optical disk apparatus is constructed for writing or reading information by irradiating a laser beam onto an optical disk while rotating the optical disk under a focus control of the laser beam relative to the rotated optical disk. In the optical disk apparatus, an irradiating section is operated to irradiate a laser beam onto the optical disk. A determining section determines a process pattern of the focus control by operating the irradiating section to irradiate the laser beam onto a predetermined area of the optical disk and by monitoring the laser beam reflected back from the predetermined area. A focusing section performs the focus control to regulate a spot diameter of the laser beam based on the determined process pattern during either of the writing or reading of information.

BACKGROUND OF THE INVENTION

[0001] 1. [Industrial Field of Utilization]

[0002] The present invention relates to an optical disk apparatus, whichirradiates an optical disk with a laser beam, a focus control methodthereof, and a computer program used for the focus control method.

[0003] 2. [Prior Art]

[0004] Recordable optical disks such as CD-R (Compact Disc-Recordable)and CD-RW (Compact Disc-Rewritable) have been available in the priorart. When various data such as music data are recorded on these opticaldisks, optical disk recording/reproducing apparatuses such as CD-R orCD-RW drive units are used. These optical disk recording/reproducingapparatuses carry out information recording by irradiating a recordingface formed on one side of an optical disk with laser beam from anoptical pickup according to information to be recorded. On the otherhand, when information recorded on the optical disk is read out, laserbeam is also irradiated from the optical pickup to read the informationfrom the return light of the laser beam reflected back from the recordface of the optical disk.

[0005] When irradiating laser beam on the recording face of the opticaldisk, the optical disk recording apparatuses perform focus control sothat the laser beam of a desirable spot diameter will be irradiated onthe recording face. In this focus control operation, return light of thelaser beam irradiated on the recording face of the optical disk isreceived, and focus control is performed using an astigmatic method.

[0006] The above-mentioned focus control in a conventional optical diskrecording apparatus is feedback control in which a return light of thelaser beam irradiated on an optical disk is acquired to perform thefocus control based on the return light acquired. Therefore, if thelaser beam is irradiated to an area with no reflecting face formed onit, a sufficient amount of return light cannot be obtained to disablethe focus control.

[0007] For example, suppose that a thermo-sensitive face is provided onan optical disk on the side opposite to a recording face on which musicdata or the like is recorded. Suppose further that the thermo-sensitiveface is irradiated with laser beam to discolor the thermo-sensitive faceso that a character image such as a music title of music data will beformed. In this case, since the laser beam has to be irradiated on thethermo-sensitive face from which an amount of reflected light equal toor larger than that from the recording face cannot be obtained, accuratefocus control cannot be performed.

SUMMARY OF THE INVENTION

[0008] The present invention has been made in view of theabove-mentioned circumstances, and it is an object thereof to provide anoptical disk apparatus, and a focus control method and program, capableof performing accurate focus control even when a laser beam isirradiated to an area of an optical disk from which a sufficient amountof reflected light of the laser beam cannot be obtained.

[0009] To solve the above-mentioned problem, according to the presentinvention, an optical disk apparatus is constructed for writing orreading information by irradiating a laser beam onto an optical diskwhile rotating the optical disk under a focus control of the laser beamrelative to the rotated optical disk. The inventive optical diskapparatus comprises an irradiating section that is operated to irradiatea laser beam onto the optical disk, a determining section thatdetermines a process pattern of the focus control by operating theirradiating section to irradiate the laser beam onto a predeterminedarea of the optical disk and by monitoring the laser beam reflected backfrom the predetermined area, and a focusing section that performs thefocus control to regulate a spot diameter of the laser beam based on thedetermined process pattern during either of the writing or reading ofinformation.

[0010] Preferably, the determining section operates the irradiatingsection to irradiate the laser beam along a predetermined round areaduring at least one turn of the optical disk, and monitors the laserbeam reflected back from the predetermined round area so as to determineone round process pattern of the focus control in function of an angularposition of the rotated optical disk. Then, the focusing sectionperforms the focus control based on the determined one round processpattern in response to the angular position of the rotated optical disk.

[0011] Practically, the determining section determines a process patternof the focus control based on a first round process pattern obtainedfrom the laser beam reflected back from an innermost round area of theoptical disk and a second round process pattern obtained from the laserbeam reflected back from an outermost round area of the optical disk.Further, the determining section determines the process pattern of thefocus control by interpolating the first round process pattern and thesecond round process pattern in terms of a radial position of the laserbeam. Then, the focusing section performs the focus control based on thedetermined process pattern in response to the radial position of thelaser beam.

[0012] Practically, the inventive optical disk apparatus furthercomprises a mount section that can rotatably mount an optical diskhaving a recording face writeable with data information and athermo-sensitive face opposite to the recording face and writeable withimage information, and an image forming section operative when theoptical disk is mounted to expose the thermo-sensitive face foroperating the irradiating section to irradiate the laser beam onto thethermo-sensitive face to thereby form the image information. In thiscase, the determining section determines the process pattern of thefocus control such that the spot diameter of the laser beam irradiatedonto the thermo-sensitive face is regulated greater than the spotdiameter of the laser beam irradiated onto the recording face.Expediently, the inventive optical disk apparatus further comprises areading section that operates the irradiating section to irradiate thelaser beam onto the thermo-sensitive face of the optical disk to readtherefrom the image information.

[0013] According to this structure, even when the information recordingand reading are performed by irradiating the laser beam on alow-reflective face of the optical disk, the focus control can beperformed according to the process pattern of focus control determinedby the determining section, rather than based on the actual return lightfrom the recording face. The process pattern of focus control determinedby the determining section is based on the return light obtained byirradiating the laser beam to the predetermined area of the opticaldisk. The predetermined area of the optical disk is set to ahigh-reflective area of the optical disk, and therefore a sufficientamount of return light can be obtained. In this case, the processpattern of focus control determined based on this result becomessuitable for any optical disk set in the optical disk apparatus.Consequently, even when the laser beam is irradiated to a low-reflectivearea, accurate focus control can be performed.

[0014] According to the present invention, there is provided a method offocus control of a laser beam relative to an optical disk rotated in anoptical disk apparatus for writing or reading information by irradiationof the laser beam onto the rotated optical disk. The inventive methodcomprises the steps of provisionally irradiating the laser beam onto apredetermined area of the optical disk, monitoring the laser beamreflected back from the predetermined area to detect a variation of aspot diameter of the laser beam, determining a process pattern of thefocus control based on the detected variation of the spot diameter,conducting the irradiation of the laser beam onto the rotated opticaldisk for writing or reading information, and performing the focuscontrol to regulate a spot diameter of the laser beam based on thedetermined process pattern during conducting the irradiation of thelaser beam. The predetermined process pattern indicates an outline,contour or profile of the focus control, which should be followed by theoptical disk apparatus for regulating the spot diameter of the laserbeam during the information writing or reading operation. The processpattern of the focus control is provisionally obtained by testirradiation or trial irradiation of the laser beam.

[0015] According to the present invention, there is provided a programfor use in an optical disk apparatus having a processor for writing orreading information by irradiation of a laser beam onto an optical diskwhile rotating the optical disk under a focus control of the laser beamrelative to the rotated optical disk. The program may be stored in amachine readable medium for loading into the optical disk apparatus. Theinventive program is executable by the processor for causing the opticaldisk apparatus to perform a focus control process comprising the stepsof provisionally irradiating the laser beam onto a predetermined area ofthe optical disk, monitoring the laser beam reflected back from thepredetermined area to detect a variation of a spot diameter of the laserbeam, determining a process pattern of the focus control based on thedetected variation of the spot diameter, conducting the irradiation ofthe laser beam onto the rotated optical disk for writing or readinginformation, and performing the focus control to regulate a spotdiameter of the laser beam based on the determined process patternduring conducting the irradiation of the laser beam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a side sectional view schematically showing thestructure of an optical disk on which an optical diskrecording/reproducing apparatus according to one preferred embodiment ofthe present invention can form a visible image.

[0017]FIG. 2 is a block diagram showing the structure of the opticaldisk recording/reproducing apparatus according to the embodiment of thepresent invention.

[0018]FIG. 3 is a diagram showing a structure of an optical pickup as acomponent of the optical disk recording/reproducing apparatus.

[0019]FIG. 4 is a diagram for explaining contents of image data used bythe optical disk recording/reproducing apparatus for formation of avisible image on a thermo-sensitive face of the optical disk.

[0020]FIG. 5 is a diagram for explaining irradiation control of laserbeam, representing the density gradation of the image when formed on thethermo-sensitive face by the optical disk recording/reproducingapparatus.

[0021]FIG. 6 is a diagram for explaining a control method of laser beamwhen the optical disk recording/reproducing apparatus forms the visibleimage on the thermo-sensitive face of the optical disk.

[0022]FIG. 7 is a diagram for explaining the control of laser power by alaser power control circuit as a component of the optical diskrecording/reproducing apparatus.

[0023]FIG. 8 is a diagram showing FG pulses generated according to theamount of rotation of a spindle motor by a frequency generator as acomponent of the optical disk recording/reproducing apparatus, and aclock signal generated based on the FG pulses.

[0024]FIG. 9 is a flowchart for explaining the operation of the opticaldisk recording/reproducing apparatus.

[0025]FIG. 10 is a flowchart for explaining the operation of the opticaldisk recording/reproducing apparatus.

[0026]FIG. 11 is a diagram showing a disk ID recorded on thethermo-sensitive face of the optical disk.

[0027]FIG. 12 is a diagram showing the area structure of thethermo-sensitive face of the optical disk.

[0028]FIG. 13 is a diagram showing a spot shape of return light of laserbeam received by a light-receiving element of the optical pickup of theoptical disk recording/reproducing apparatus.

[0029]FIG. 14 is a diagram for explaining a process pattern of focuscontrol adapted in the optical disk recording/reproducing apparatus.

[0030]FIG. 15 is a diagram for explaining a method of deriving theprocess pattern of focus control determined by test irradiationperformed by the optical disk recording/reproducing apparatus.

[0031]FIG. 16 is a diagram for explaining the size of a beam spotdiameter of a laser beam irradiated on the thermo-sensitive face of theoptical disk by means of the optical pickup of the optical diskrecording/reproducing apparatus.

[0032]FIG. 17 is a timing chart for explaining the operation of theoptical disk recording/reproducing apparatus when irradiating a laserbeam on the thermo-sensitive face of the optical disk to form a visibleimage.

[0033]FIG. 18 is a diagram showing the thermo-sensitive face of theoptical disk after irradiated with laser beam by the optical diskrecording/reproducing apparatus.

[0034]FIG. 19 is a block diagram showing a structure of a modificationof the optical disk recording/reproducing apparatus according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] Embodiments of the present invention will now be described withreference to the accompanying drawings.

[0036] A. Structure of Embodiment

[0037] The present invention provides an optical diskrecording/reproducing apparatus for irradiating laser beam on arecording face of an optical disk to record information. The opticaldisk recording/reproducing apparatus has not only the function forrecording information on the recording face, but also a function forforming a visible image corresponding to image data by irradiating laserbeam on a thermo-sensitive face of the optical disk, thethermo-sensitive face being formed on the side opposite to the recordingface. The following describes the structure of an optical disk on whichthe formation of such a visible image is possible, and then thestructure of an optical disk recording/reproducing apparatus capable ofcarrying out information recording and formation of a visible image onthe optical disk.

[0038] A-1. Structure of Optical Disk

[0039]FIG. 1 is a side sectional view showing the structure of adisk-shaped optical disk capable of recording information on one sideand forming a visible image on the other side. As shown in FIG. 1, theoptical disk D has a protective layer 201, a recording layer (recordingface) 202, a reflective layer 203, a protective layer 204, athermo-sensitive layer (thermo-sensitive face) 205, and a protectivelayer 206. These layers are laminated in this order. It should be notedthat the figure schematically shows the structure of the optical disk D,and the ratio of dimensions or the like between the layers isexaggerated.

[0040] A groove (guide groove) 202 a is formed on the recording layer202 in a spiral shape. When information is recorded on the optical diskD, laser beam is irradiated along the groove 202 a. Therefore, wheninformation is recorded, the top face (hereinbelow, called the recordingface) on the side of the protective layer 201 (the upper side in thefigure) of the optical disk D is set to face an optical pickup of theoptical disk recording/reproducing apparatus. In this case, the laserbeam irradiated from the optical pickup is moved along the groove 202 ato record the information. On the other hand, when a visible image isformed on the back face of the optical disk D, the optical disk D is soset that the back face (hereinbelow, called the thermo-sensitive face)on the side of the protective layer 206 faces the optical pickup of theoptical disk recording/reproducing apparatus according to the presentinvention. Then the laser beam is irradiated to the thermo-sensitivelayer 205 to thermally discolor a desirable position of thethermo-sensitive layer 205, thus forming the visible image. As mentionedabove, since the optical disk D has almost the same structure as theconventionally used CD-R, except that the thermo-sensitive layer 205 isprovided, detailed descriptions of the other layers such as therecording layer 202 will be omitted. In the specification, the term“thermo-sensitive face” denotes a face varying in color when irradiatedwith laser beam. This face is formed from the thermo-sensitive layer 205having such color varying properties.

[0041] A-2. Structure of Optical Disk Recording/Reproducing Apparatus

[0042]FIG. 2 is a block diagram showing the structure of the opticaldisk recording/reproducing apparatus according to one embodiment of thepresent invention. As shown, the optical disk recording/reproducingapparatus 100 is connected to a host personal computer (PC) 110. Theoptical disk recording/reproducing apparatus 100 includes an opticalpickup 10, a spindle motor 11, an RF (Radio Frequency) amplifier 12, aservo circuit 13, a decoder 15, a control unit 16, an encoder 17, astrategy circuit 18, a laser driver 19, a laser power control circuit20, a frequency generator 21, a stepping motor 30, a motor driver 31, amotor controller 32, a PLL (Phase Locked Loop) circuit 33, a FIFO (FirstIn First Out) memory 34, a driving pulse generator 35, and a buffermemory 36.

[0043] The spindle motor 11 is provided for driving the optical disk Dto rotate for data recording. The servo circuit 13 controls the RPM(Revolutions Per Minute) of the spindle motor 11. In the embodiment,since the optical disk recording/reproducing apparatus 100 carries outrecording and the like by a CAV (Constant Angular Velocity) method, thespindle motor 11 runs at a constant angular speed set on theinstructions of the control unit 16 or the like.

[0044] The optical pickup 10 is a unit for irradiating laser beam to theoptical disk D rotated by the spindle motor 11. FIG. 3 shows thearrangement of the optical pickup 10. As shown, the optical pickup 10includes a laser diode 53 for outputting laser beam B, a diffractiongrating 58, an optical system 55 for condensing and focusing the laserbeam B on the face of the optical disk D, and a light-receiving element56 for receiving reflected light of the laser beam.

[0045] In the optical pickup 10, the laser diode 53 is supplied withdriving current from the laser driver 19 (see FIG. 2) to output thelaser beam B of certain intensity corresponding to the driving current.The optical pickup 10 divides the laser beam B outputted from the laserdiode 53 into a main beam, a preceding beam, and a following beam bymeans of the diffraction grating 58, and passes the three laser beamsthrough a polarization beam splitter 59, a collimator lens 60, a ¼wavelength plate 61, and an objective lens 62 to focus the laser beam onthe face of the optical disk D. Then the optical pickup 10 repasses thethree laser beams reflected from the optical disk D through theobjective lens 62, the ¼ wavelength plate 61, and the collimator lens60, reflects them on the polarization beam splitter 59, and makes thereflected light incident on the light-receiving element 56 through acylindrical lens 63. The light-receiving element 56 outputs a signal ofthe received light to the RF amplifier 12 (see FIG. 2). The receivedlight signal is supplied to the control unit 16 and the servo circuit 13through the RF amplifier 12.

[0046] The objective lens 62 is held by a focus actuator 64 and atracking actuator 65 so that it can move in the direction of the opticalaxis of the laser beam B and the direction of the radius of the opticaldisk D. The focus actuator 64 and the tracking actuator 65 move theobjective lens 62 in the direction of the optical axis and the directionof the radius in response to a focus error signal and a tracking errorsignal from the servo circuit 13 (see FIG. 2), respectively. Supposethat the laser beam is irradiated on the recording face of the opticaldisk D, for example, data is recorded on a common CD-R or suppose thatthe laser beam is irradiated for reading data from a CD-ROM. In such acase, the servo circuit 13 generates the focus error signal and thetracking error signal based on a received light signal supplied throughthe light-receiving element 56 and the RF amplifier 12, so that theobjective lens 62 is moved, thereby performing focus control andtracking control, that is, feedback control. On the other hand, when thelaser beam is irradiated on a low-reflective face such as thethermo-sensitive face of the optical disk D, the servo circuit 13carries out open-loop focus control according to the process pattern offocus control determined by the control unit 16 as described later,rather than the feedback control based on the return light.

[0047] The optical pickup 10 also has a front monitor diode, not shown,through which a current is passed while the laser diode 53 is outputtingthe laser beam. The current is supplied from the optical pickup 10 tothe laser power control circuit 20 shown in FIG. 2.

[0048] The RF amplifier 12 amplifies an RF signal that has beensubjected to EFM (Eight-to-Fourteen Modulation) and supplied form theoptical pickup 10, and outputs the amplified RF signal to the servocircuit 13 and the decoder 15. Upon reproduction, the decoder 15EFM-demodulates the EFM-modulated RF signal supplied from the RFamplifier 12 to generate reproduced data.

[0049] The servo circuit 13 is supplied with a control signal from thecontrol unit 16, an FG pulse signal of a frequency corresponding to theRPM of the spindle motor 11 and supplied from the frequency generator21, and the RF signal from the RF amplifier 12. Based on the signalssupplied, the servo circuit 13 performs rotation control of the spindlemotor 11, focus control and tracking control of the optical pickup 10.As mentioned above, when the laser beam is irradiated to alow-reflective area, the RF signal is not used for the focus control.Further, when a visible image is formed on the thermo-sensitive face ofthe optical disk D, unlike when recording is performed on the recordingface, it is unnecessary to trace irradiation positions along thepreformed groove (guide groove) or the like. Therefore, in theembodiment, the target value for tracking control is fixed (that is, aconstant offset voltage is set for the tracking actuator).

[0050] The driving method for the spindle motor 11 when information isrecorded on the recording face (see FIG. 1) of the optical disk D orwhen a visible image is formed on the thermo-sensitive face (see FIG. 1)of the optical disk D may be either a method of driving the optical diskD with a constant angular speed (CAV: Constant Angular Velocity) or amethod of driving the optical disk D to rotate at a constant linearrunning speed (CLV: Constant Linear Velocity). The optical diskrecording/reproducing apparatus 100 according to the embodiment employsthe CAV method, and the servo circuit 13 drives the spindle motor 11 torun at a constant angular speed specified by the control unit 16.

[0051] The buffer memory 36 stores information to be recorded on therecording face of the optical disk D (hereinbelow, called recordingdata) and information corresponding to a visible image to be formed onthe thermo-sensitive face of the optical disk D (hereinbelow, calledimage data), both of which are supplied from the host PC 110. Therecording data stored in the buffer memory 36 is outputted to theencoder 17, and the image data is outputted to the control unit 16.

[0052] The encoder 17 EFM-modulates the recording data supplied from thebuffer memory 36, and outputs it to the strategy circuit 18. Thestrategy circuit 18 performs time-base correction and the like for theEFM signal supplied from the encoder 17, and outputs it to the laserdriver 19.

[0053] The laser driver 19 drives the laser diode 53 (see FIG. 3) of theoptical pickup 10 based on the signal modulated according to therecording data and supplied from the strategy circuit 18 under thecontrol of the laser power control circuit 20.

[0054] The laser power control circuit 20 controls the power of thelaser beam irradiated from the laser diode 53 (see FIG. 3) of theoptical pickup 10. Specifically, the laser power control circuit 20controls the laser driver 19 so that a laser beam having a certain powerequal to a target value for the optimum laser power specified by thecontrol unit 16 will be irradiated from the optical pickup 10. The laserpower control by the laser power control circuit 20 is feedback controlusing a current value supplied from the front monitor diode of theoptical pickup 10 to irradiate laser beam of the target intensity fromthe optical pickup 10.

[0055] The image data supplied from the host PC 110 and stored in thebuffer memory 36 is supplied through the control unit 16, andsequentially stored in the FIFO memory 34. The image data stored in theFIFO memory 34, that is, the image data supplied from the host PC 110 tothe optical recording/reproducing device 100 contains the followinginformation. Since the image data is to form a visible image on the faceof the disk-shaped optical disk D, it describes, as shown in FIG. 4,information indicative of a gradient (density) at each of n coordinatepoints (indicated with black dots in the figure) on many concentriccircles arranged about the center O of the optical disk D. The imagedata describes such information that indicates a gradient at each of thecoordinate points on the concentric circles in the order from theinnermost circle to outermost circle, that is, from coordinate pointsP11, P12, . . . , P1n belonging to the innermost circle, coordinatepoints P21, P22, . . . , P2n belonging to the next innermost circle,coordinate points belonging intermediate circled, to a coordinate pointPmn on the outermost circle. Thus the information on the gradient ateach coordinate point on such polar coordinates is supplied to the FIFOmemory 34 in the above-mentioned order. It should be noted that FIG. 4is a schematic diagram for clearly showing the positional relationshipbetween coordinate points, and actual coordinate points are more crowdedthan those shown. Further, if the image data to be formed on thethermo-sensitive face of the optical disk D is created in the host PC110 in a commonly used format such as the bitmap format, the host PC 110will have only to convert the bitmap data to polar coordinate data. Theconverted image data is sent from the host PC 110 to the optical diskrecording/reproducing apparatus 100.

[0056] Then, when a visible image is formed on the thermo-sensitive faceof the optical disk D based on the image data supplied, a clock signalfor image recording is supplied from the PLL circuit 33 to the FIFOmemory 34. The FIFO memory 34 outputs to the driving pulse generator 35information indicative of a gradient at a coordinate point in the orderfrom the earliest stored one each time a clock pulse of the clock signalfor image recording is supplied.

[0057] The driving pulse generator 35 generates a driving pulse forcontrolling the irradiation timing of laser beam from the optical pickup10 when the visible image is formed on the thermo-sensitive face of theoptical disk D. In this case, the driving pulse generator 35 generates adriving pulse of certain pulse width corresponding to the informationindicative of the gradient at each coordinate point supplied from theFIFO memory 34. For example, when the gradient at a certain coordinatepoint is relatively large (when density is high), such a driving pulsethat the pulse width of write level is set to a large value is generatedas shown in the upper side of FIG. 5. On the other hand, when it isrelatively small, such a driving pulse that the pulse width of writelevel is set to a small value is generated as shown in the lower side ofFIG. 5. The term “write level” denotes a power level of laser enough tomake the thermo-sensitive face (thermo-sensitive layer 205) obviouslydiscolored when such a power level of laser is irradiated on thethermo-sensitive face of the optical disk D. When such a driving pulseis supplied to the laser driver 19, laser beam of the write level isirradiated from the optical pickup 10 during a period of timecorresponding to the pulse width. Therefore, the larger the gradient,the longer the irradiation time of the laser beam of the write level. Inthis case, since the discolored area in a unit area of thethermo-sensitive face of the optical disk D becomes larger, the userperceives that this area is highly dense. In the embodiment, the lengthof the discolored area per unit area (unit length) is varied torepresent the gradient indicated in the image data. Here, the term“servo level” denotes a power level at which the thermo-sensitive faceremains about the same when laser of this power level is irradiated onthe thermo-sensitive face of the optical disk D. Therefore, the laserbeam of the servo level, rather than the laser beam of the write level,can be irradiated to an area unnecessary to be discolored.

[0058] The driving pulse generator 35 thus generates the driving pulseaccording to the information indicative of the gradient at eachcoordinate point. In addition, the driving pulse generator 35 may inserta pulse of the write level or servo level for a very short time periodwhen required for laser power control by the laser power control circuit20, or focus control and tracking control by the servo circuit 13. Forexample, as shown in the upper side of FIG. 6, suppose that the laserbeam of the write level needs to be irradiated for a period of time T1so that the visible image will be represented according to the gradientat a coordinate point in the image data. In this case, if the period oftime T1 is longer than a predetermined servo period ST for controllingthe laser power, a servo-off pulse (SSP1) is inserted for a very shorttime t when the servo period ST has elapsed after the pulse of the writelevel was generated. On the other hand, as shown in the lower side ofFIG. 6, suppose that the laser beam of the servo level needs to beirradiated for a period longer than the servo period ST so that thevisible image will be represented according to the gradient at acoordinate point in the image data. In this case, a servo-on pulse(SSP2) is inserted when the servo period ST has elapsed since the pulseof the servo level was generated.

[0059] As mentioned above, the laser power control by the laser powercontrol circuit 20 is carried out based on the current (of a valuecorresponding to the intensity of the laser beam irradiated) suppliedfrom the front monitor diode that has received the laser beam irradiatedfrom the laser diode 53 (see FIG. 3) of the optical pickup 10. To bemore specific, as shown in FIG. 7, the laser power control circuit 20samples and holds a value corresponding to the intensity of irradiatedlaser beam received by such a front monitor diode 53 a (S201 and S202).Then, based on the result of the sample-and-hold operation performedwhile the laser beam is being irradiated at the write level as thetarget value, that is, while a driving pulse of the write level is beinggenerated (see FIGS. 5 and 6), the laser power control is so performedthat the laser beam of the target write level value supplied from thecontrol unit 16 is irradiated (S203). On the other hand, based on theresult of the sample-and-hold operation performed while the laser beamis being irradiated at the servo level as the target value, that is,while a driving pulse of the servo level is being generated (see FIGS. 5and 6), the laser power control is so performed that the laser beam ofthe target servo-level value supplied from the control unit 16 isirradiated (S204). Consequently, when a pulse of the write level orservo level is not continuously outputted for a period of time longerthan the predetermined servo period (sample period) ST, the servo-offpulse SSP1 or the servo-on pulse SSP2 is forcibly inserted in the mannermentioned above, irrespective of the contents of the image data. Thusthe laser power control can be performed for each level.

[0060] It is preferable that the time at which the servo-off pulse SSP1or the servo-on pulse SSP2 is inserted be as short as possible in such arange that the laser power control can be performed without any trouble.Since the insertion time is set very short, the formation of the visibleimage is barely affected, thus performing the above-mentioned servooperation.

[0061] Returning to FIG. 2, the PLL circuit 33 multiplies the FG pulsesignal of a frequency supplied from the frequency generator 21 ascorresponding to the RPM of the spindle motor 11 to output a clocksignal used for formation of the visible image as described later. Thefrequency generator 21 outputs the FG pulse signal of the frequencycorresponding to the RPM of the spindle motor 11 usingcounter-electromotive current obtained by the motor driver of thespindle motor 11. For example, as shown in the upper side of FIG. 8, ifthe frequency generator 21 generates eight FG pulses during one turn ofthe spindle motor 11, that is, during one turn of the optical disk D,the PLL circuit 33 outputs a clock signal obtained by multiplying the FGpulses (e.g., a frequency five times the FG pulse signal, that is, 40pulses of H level during one turn of the optical disk D). In otherwords, it outputs the clock signal of a frequency corresponding to therotational speed of the optical disk D rotated by the spindle motor 11.The clock signal thus obtained by multiplying the FG pulse signal isoutputted from the PLL circuit 33 to the FIFO memory 34. Then, dataindicating the gradient at a coordinate point is outputted from the FIFOmemory 34 to the driving pulse generator 35 in each cycle of the clocksignal, that is, each time the disk D is rotated to a fixed angle.Although the PLL circuit 33 is used to multiply the FG pulses andgenerate the clock signal, if a motor having sufficiently stable drivingpower is used as the spindle motor 11, a crystal oscillator may beprovided instead of the PLL circuit 33 to multiply the FG pulses andgenerate the clock signal, that is, the clock signal of a frequencycorresponding to the rotational speed of the optical disk D.

[0062] The stepping motor 30 is an actuator for moving the opticalpickup 10 in the radial direction of the optical disk D set in theoptical disk apparatrus. The motor driver 31 drives the stepping motor30 to run by an amount corresponding to the pulse signal supplied fromthe motor controller 32. The motor controller 32 generates a pulsesignal according to the traveling direction and the amount of travel ofthe optical pickup 10 in the direction of the radius of the optical diskD in accordance with travel start instructions, including the movingdirection and the amount of travel, from the control unit 16. Then themotor controller 32 outputs the generated pulse signal to the motordriver 31. The stepping motor 30 moves the optical pickup 10 in theradial direction of the optical disk D, while the spindle motor 11rotates the optical disk D. It allows the optical pickup 10 to changeits irradiation position of laser beam to various positions.

[0063] The control unit 16 is constituted of a CPU (Central ProcessingUnit), a ROM (Read Only Memory), a RAM (Random Access Memory), and thelike. The control unit 16 controls each part of the optical diskrecording/reproducing apparatus 100 according to a program stored in theROM to centrally control recording on the recording face of the opticaldisk D and image formation on the thermo-sensitive face of the opticaldisk D including focus control characteristic of the present invention.

[0064] The above describes the structure of the optical diskrecording/reproducing apparatus 100 according to the embodiment of thepresent invention.

[0065] B. Operation of Embodiment

[0066] The operation of the optical disk recording/reproducing apparatus100 will be described next. As described above, the optical diskrecording/reproducing apparatus 100 can record, on the recording face ofthe optical disk D, information such as music data supplied from thehost PC 110, and form, on the thermo-sensitive face of the optical diskD, a visible image corresponding to image data supplied from the host PC110. Referring to FIGS. 9 and 10, the operation of the optical diskrecording/reproducing apparatus 100 capable of information recording andformation of a visible image will be described below.

[0067] At fist, when the optical disk D is set in the optical diskrecording/reproducing apparatus 100, the control unit 16 controls theoptical pickup 10 and the like to detect whether ATIP (Absolute Time InPregroove) information is recorded on the optical disk D of the sidefacing the optical pickup 10 (step Sa1). It is common knowledge that theATIP information is information prerecorded in the pregroove on therecording face of a CD-R. When the ATIP information is recorded, itshows that the recording face of the optical disk D is set to face theoptical pickup 10. On the other hand, when the ATIP information is notrecorded, it shows that the thermo-sensitive face of the optical disk Dis set to face the optical pickup 10. In other words, the control unit16 detects the presence or absence of the ATIP information to detectwhich side of the optical disk D is set to face the optical pickup 10.Instead of the method of detecting which side is set to face the opticalpickup 10 by detecting the presence or absence of the ATIP information,any other method may be used. For example, the user may input that thethermo-sensitive face has been set to face the optical pickup 10.

[0068] When detecting the ATIP information from the optical disk D, thecontrol unit 16 determines that the optical disk D is so set that therecording face faces the optical pickup 10, and performs control forrecording, on the recording face, recording data supplied from the hostPC 110 (step Sa2). The control for recording the recording data iscarried out in the same manner as in the conventional optical diskrecording/reproducing apparatus (CD-R drive unit). In addition, thefocus control is also normal feedback control based on return light.Therefore, the descriptions of these control operations will be omitted.

[0069] On the other hand, when not detecting the ATIP information fromthe optical disk D, the control unit 16 determines that thethermo-sensitive face is set to face the optical pickup 10, and thendetermines whether a disk ID of the optical disk D can be acquired (stepSa3). In the embodiment, the disk ID of the optical disk D is a disk IDrecorded on the thermo-sensitive face of the optical disk D that has therecording face and the thermo-sensitive face (see FIG. 1). For example,as shown in FIG. 11, a visible image corresponding to coded informationon the disk ID is described around the circumference of the outermostcircular portion on the thermo-sensitive face of the optical disk D. Inthe embodiment, as shown, reflecting areas 301 a with lengthscorresponding to respective pieces of the code and non-reflecting areas301 b are formed around the circumference of the outermost circularportion to describe the disk ID on the thermo-sensitive face of theoptical disk D. The control unit 16 traces the irradiation positions ofthe laser beam from the optical pickup 10 around the circumference ofthe outermost circular portion of the optical disk D to acquire the diskID from the reflected light.

[0070] If the reflecting areas 301 a and the non-reflecting areas 301 bcorresponding to the disk ID are not formed in the outermost circularportion of the thermo-sensitive face, the optical disk D can be judgedto be a common optical disk (such as a CD-R) having no thermo-sensitiveface. When cannot acquire the disk ID, the control unit 16 determinesthat the optical disk D is incapable of forming any visible image (stepSa4) and performs processing such as to inform the user of it.

[0071] On the other hand, when acquiring the disk ID from the opticaldisk D, the control unit 16 waits for instructions for image formationincluding image data from the host PC 110 (step Sa5). Upon receipt ofthe instructions for image formation, the control unit 16 performsinitialization control for forming a visible image on thethermo-sensitive face of the optical disk D (step Sa6). To be morespecific, the control unit 16 controls the servo circuit 13 to drive thespindle motor 11 to run at a predetermined angular speed.

[0072] After completion of the initialization control, the control unit16 performs processing for determining the process pattern of focuscontrol to be performed at the time of irradiation of laser beam forimage formation (step Sa7). In the processing for determining theprocess pattern of focus control, the control unit 16 performs testirradiation to decide the process pattern of focus control. To conductthe test irradiation, the control unit 16 sends an instruction to themotor controller 32 to move the optical pickup 10 so that the laser beamwill be irradiated to the innermost circular round area Da of theoptical disk D shown in FIG. 12, and drives the stepping motor 30.Unlike the recording face, the reflectivity of the thermo-sensitive faceof the optical disk D is normally low. However, this optical disk D isdesigned such that the innermost circular area Da and the outermostcircular area Db have high reflectivity, and in order to perform thetest irradiation of laser beam to these round areas, the irradiationposition of laser beam from the optical pickup 10 is moved first to theinnermost round area Da in the manner mentioned above.

[0073] After moving the position of the optical pickup 10 as mentionedabove, the control unit 16 instructs the optical pickup 10 to conducttest irradiation of laser beam during one turn of the optical disk D.The control unit 16 also instructs the servo circuit 13 to perform focuscontrol based on the return light, that is, normal focus control whenthe laser beam is thus irradiated during one turn of the optical disk D.

[0074] The control unit 16 acquires the contents of the focus controlperformed by the servo circuit 13 based on the return light receivedduring one turn of the optical disk D. The control unit 16 then storesthe actual contents of the focus control, that is, the contents of thefocus control obtained by changing the variable of the focus actuator bya predetermined amount, in the RAM or the like in synchronization withthe clock signal supplied from the PLL circuit 33.

[0075] To be more specific, as shown in FIG. 13, the focus control atthe time of the test irradiation is performed based on a signaloutputted from the light-receiving element 56 of the optical pickup 10using an astigmatic method like normal feedback focus control. In otherwords, the servo circuit 13 drives the focus actuator 64 (see FIG. 3) sothat a circular spot of return light will be received at the center offour areas 56 a, 56 b, 56 c, and 56 d of the light-receiving element 56as shown in FIG. 13 (A in the figure). If the amount of light receivedon each area 56 a, 56 b, 56 c, or 56 d is a, b, c, or d, the drivingamount of the focus actuator 64 (driving voltage applied to theactuator) is so controlled that the focus error determined from(a+c)−(b+d) becomes zero. In this case, like the normal feedback focuscontrol, the driving amount of the focus actuator 64 is so determinedthat spot A shown in FIGS. 13 and 14 is received (that is, a beam of thesmallest spot diameter is irradiated on the optical disk D).

[0076] The rated contents of the focus control obtained by changing theorigins contents of the focus control by a predetermined amount duringone turn of the optical disk D are stored in a storage area as a processpattern of inner focus control in the RAM in synchronization with eachclock pulse of the clock signal generated by the PLL circuit 33 duringone turn of the optical disk D. In other words, as schematically shownas dot-dash line in FIG. 15, the rated or adjusted contents of the focuscontrol (actuator driving voltage) obtained by reduing the originalcontents of the focus control actually performed each time each clockpulse of the clock signal is generated are stored in association withthe clock pulse. Although the figure shows 16 clock pulses for the sakeof simplification, the number of clock pulses is not limited to thisnumber. Further, when stored, the contents of the focus control may notbe necessarily associated with all the clock pulses generated. Forexample, the contents of the focus control may be stored in associationwith a clock pulse at constant intervals of clock pulses (or FG pulses)such as every three or four clock pulses.

[0077] Since the clock pulses of the clock signal are pulses obtained bymultiplying the FG pulses supplied from the frequency generator 21, theyare generated each time the optical disk D is rotated by a predeterminedangular amount. For example, if the number of clock pulses generatedduring one turn of the optical disk D is 360, one clock pulse isgenerated each time the optical disk D is rotated one degree. In otherwords, the above-mentioned contents of the focus control are stored asone round process pattern of the focus control in association with clockpulses every predetermined amount of rotation (e.g., one degree) of theoptical disk D.

[0078] As mentioned above, the contents of the focus control stored inthe storage area for inner focus control are the process pattern offocus control with a predetermined amount of adjustment, not theoriginal contents of the focus control performed at the time of the testirradiation of the laser beam. Referring next to FIG. 14, a descriptionwill be made of the predetermined adjective amount. As shown, the focuscontrol performed at the time of the test irradiation of the laser beamis to control the laser beam irradiated on the face of the optical diskD, in the same manner as normal focus control, so that the spot diameterwill be the smallest. On the other hand, when a visible image is formedon the thermo-sensitive face of the optical disk D, the optical diskrecording/reproducing apparatus 100 of the embodiment performs suchfocus control that the thermo-sensitive face is irradiated with laserbeam whose spot diameter is larger than that irradiated at the time ofinformation recording on the recording face. To be more specific, thefocus control is so performed that the spot diameter Z shown in FIG. 14can be obtained for the image formation. For this reason, a focusactuator driving voltage obtained by adjusting the original focusactuator driving voltage as the original contents of the focus controlactually performed in the manner mentioned above is stored as theprocess pattern of the focus control for the image formation. Theadjustment or correction is made to compensate for a predeterminedoffset voltage Vd.

[0079] The focus control is performed according to the process patternof the focus control thus stored. Upon formation of a visible image,laser beam of a spot diameter larger than those of the normal recordingand reading is irradiated on the thermo-sensitive face. When the visibleimage is formed on the thermo-sensitive face of the optical disk D inthe manner mentioned above, since laser beam of a spot diameter largerthan that at the time of information recording on the recording face isirradiated, the following effects can be obtained. In the embodiment,even when the visible image is formed, laser beam is irradiated whilerotating the optical disk D in the same manner when information isrecorded on the recording face. Therefore, setting the spot diameter ofthe laser beam large makes it possible to form the visible image overthe entire area of the thermo-sensitive face of the optical disk D in ashorter time. The reason for this will be described with reference toFIG. 16. As schematically shown, a comparison between large and smallbeam spot diameters BS of laser beam shows that the area of a targetarea for image formation during one turn of the optical disk D becomeslarge when the beam spot diameter BS is large. This means that when thebeam spot diameter BS is small, the optical disk D needs to be rotatedabout more turns in order to cover the entire area for the imageformation (in the figure, four turns when BS is large and six turns whenBS is small), and it takes longer time for the image formation. For sucha reason, upon formation of a visible image, the optical diskrecording/reproducing apparatus 100 irradiates laser beam of a spotdiameter larger than that at the time of information recording.

[0080] As mentioned above, the test irradiation of the laser beam to theinnermost circular area Da of the optical disk D is performed, and thecontents of the focus control are stored in the storage area for theround process pattern of inner focus control in the RAM in associationwith the clock pulses. After that, the control unit 16 sends aninstruction to the motor controller 32 to move the optical pickup 10 sothat the laser beam will be irradiated to the outermost circular area Dbof the optical disk D shown in FIG. 12, and drives the stepping motor30.

[0081] After that, the control unit 16 instructs the optical pickup 10to perform test irradiation of laser beam during one turn of the opticaldisk D in the same manner as the test irradiation to the area Da of theoptical disk D. The control unit 16 also instructs the servo circuit 13to perform focus control based on the return light, that is, normalfeedback focus control when the laser beam is thus irradiated during oneturn of the optical disk D. When the laser beam is irradiated to theoutermost circular area Db, the control unit 16 instructs the opticalpickup 10 to start irradiation of the laser beam from position Dbscorresponding to position Das from which the irradiation of the laserbeam to the innermost circular area Da was started. In other words, asshown in FIG. 12, it instructs the start of irradiation of the laserbeam from the position Dbs of the area Db. Here, the position Dbs andthe position Das from which the irradiation of the laser beam to theinnermost circular area Da was started are on the same line drawn fromthe center O of the optical disk D in the radial direction. In thisspecification, such a position on the same line is called a referenceposition, and the FG pulses are counted to detect whether theirradiation position of the laser beam has passed the referenceposition. For example, if the number of FG pulses for one turn of theoptical disk D is eight, the point at a time when the count of eight FGpulses has reached after the irradiation of the laser beam to theinnermost circular area Da was started becomes the timing of passing thereference position. Next, the point at a time when the count of 16 FGpulses has reached also becomes the timing of passing the referenceposition. Similarly, the point at the time when the count of 8n FGpulses (where n is an integear number) has reached becomes the timing ofpassing the reference position. Thus, the irradiation of the laser beamto the outermost circular area Db can be started at this timing.

[0082] Then, the control unit 16 stores the adjusted contents of thefocus control (shown as dash line in FIG. 15) obtained by reducing theoriginal contents of the focus control actually performed when the laserbeam was irradiated to the outermost circular area Db of the opticaldisk D, that is, by changing the controlled variable of the focusactuator by an amount. The adjusted contents of the focus control thusobtained are stored in a storage area for the one round process patternof outer focus control in the RAM in synchronization with the clocksignal supplied from the PLL circuit 33.

[0083] After completion of the processing for determining the processpatterns of the focus control mentioned above, processing for formingthe visible image on the thermo-sensitive face of the optical disk D isperformed. As shown in FIG. 11, the control unit 16 transfers to theFIFO memory 34 the image data supplied from the host PC 110 through thebuffer memory 36 (step Sa8). Then, the control unit 16 determines, fromthe FG pulse signal supplied from the frequency generator 21, whether apredetermined reference position of the optical disk D rotated by thespindle motor 11 has passed the irradiation position of the laser beamfrom the optical pickup 10 (step Sa9). As mentioned above, the count ofFG pulses is started from the point in time when the irradiation of thelaser beam to the innermost circular area Da was started to detectwhether the reference position (see FIG. 12) has passed the irradiationposition of the laser beam.

[0084] When detecting that the reference position of the optical disk Dhas passed the irradiation position of the laser beam after receivingthe instructions for image formation from the host PC 110 and completingthe processing for deciding the contents of the focus control, thecontrol unit 16 increments variable R indicating the number of rotationsby one (step Sa10), and determines whether R is an odd number (stepSa11).

[0085] After completion of the processing for deciding the contents ofthe focus control, when the control unit 16 detects that the referenceposition has been passed for the first time, R=0 (initial value)+1=1. Inthis case, it is determined in step Sa10 that R is an odd number. Whendetermining that R is an odd number, the control unit 16 controls theoptical pickup 10 to irradiate the laser beam on the thermo-sensitiveface of the optical disk D and form the visible image (step Sa12). To bemore specific, from the point in time when receiving a pulse fordetecting the reference position, the control unit 16 starts control ofeach part to output the image data sequentially from the FIFO memory 34in synchronization with the clock signal outputted from the PLL circuit33. As shown in FIG. 17, the FIFO memory 34 under control outputsinformation indicative of the gradient at a coordinate point to thedriving pulse generator 35 each time each clock pulse is supplied fromthe PLL circuit 33. The driving pulse generator 35 generates a drivingpulse of a pulse width determined according to the gradient indicated inthe information, and outputs the driving pulse to the laser driver 19.As a result, the optical pickup 10 irradiates laser beam at the writelevel on the thermo-sensitive face of the optical disk D for a period oftime corresponding to the gradient at each coordinate point to discolorthe irradiated area. Thus the visible image as shown in FIG. 18 can beformed.

[0086] As schematically shown, since the optical disk D is rotated bythe spindle motor 11, the irradiation position of the laser beam fromthe optical pickup 10 is moved around the circumference by an area,indicated with “C” in the figure, in one cycle of the clock signal (fora period from rising timing of a pulse until rising timing of the nextpulse). The period of time during which the laser beam must beirradiated at the write level while passing the area C is variedaccording to the gradient in the manner mentioned above, so that thedisclosed area can be varied in each area C according to the gradientsdifferent among the areas. Thus, since the irradiation time of the laserbeam when passing each area C is controlled according to the gradient ateach coordinate point, the visible image corresponding to the image datacan be formed on the thermo-sensitive face of the optical disk D.

[0087] When the laser beam is irradiated for image formation, open-loopfocus control according to the process patterns of the focus controlstored in the RAM by the processing for determining the process patternsof the focus control, rather than the closed-loop focus control based onthe return light from the thermo-sensitive face, is performed. In otherwords, the control unit 16 decides the amount of focus control based onthe process patterns of the focus control determined as mentioned aboveand the irradiation position of the laser beam from the optical pickup10 in the radial direction to control the focus actuator 64 through theservo circuit 13.

[0088] To be more specific, the control unit 16 decides the amount offocus control V after the process patterns of the focus control inresponse to positional information indicated by counts of clock pulsefrom the reference position each detected one by one during the imageformation period. Namely, the focus control is performed according torotation amount information 0 indicating the angular amount of rotationfrom the reference position, position information r indicating theirradiation position in the radial direction, and the contents of thefocus control stored in the RAM. The amount of focus control V isdetermined according to the following equation:

V=df ×{fin (r)×in (θ)+fout (r)×out (θ)}

[0089] In the above equation, df is the ratio of defocus distribution,and it is a fixed value, for example, 0.8. fin(r) is a predeterminedfunction, and fout(r) is also a predetermined function. It is determinedwhich of, the inner focus control pattern and the outer focus controlpattern is more reflected in the focus control contents, depending onwhat kinds of functions are employed as these functions. For example, ifthe ratio of contribution between the inner and outer round processpatterns is determined in a proportional manner simply according to theposition r in the radial direction, fin(r)=(R−r)/R and fout(r)=r/R,where R is the radius of the disk D. Further, in(θ) represents the innerfocus control pattern determined as mentioned above and stored inassociation with each clock pulse corresponding to the rotation amountθ. Similarly, out(θ) represents the outer focus control pattern and isstored in association with each clock pulse corresponding to therotation amount θ. If the rotation amount θ from the reference positioncorresponds to the seventh clock pulse from the reference position asshown in FIG. 15, in(θ) is Vin and out(θ) is Vout.

[0090] The control unit 16 controls the focus actuator 64 through theservo circuit 13 so that the focus control will be performed accordingto the focus control amount V derived each time a clock pulse issupplied in the manner mentioned above (that is, each time θincrementally varies). This control makes it possible to irradiate thethermo-sensitive face of the optical disk D with laser beam of a largespot diameter as mentioned above (see FIG. 16), and hence to achievefaster image formation processing.

[0091] Upon execution of the control sequence for forming the visibleimage by the irradiation of the laser beam controlled according to theimage data, the control unit 16 returns to step Sa8 and transfers theimage data from the buffer memory 36 to the FIFO memory 34. Then, thecontrol unit 16 detects whether the irradiation position of the laserbeam from the optical pickup 10 has passed the reference position of theoptical disk D (step Sa9). When detecting that it has passed thereference position, the control unit 16 increments R by one (step Sa10).As a result, if R becomes an even number, the control unit 16 controlseach part of the device to stop the formation of the visible image bythe irradiation control of the laser beam (step Sa13). To be morespecific, the control unit 16 controls the FIFO memory 34 not to outputthe information indicative of the gradient at each coordinate point tothe driving pulse generator 35 in synchronization with the clock signalsupplied from the PLL circuit 33. In other words, after irradiating thethermo-sensitive face of the optical disk D with the laser beam of thewrite level and completing the formation of the visible image, thecontrol unit 16 performs such control that the irradiation of the laserbeam for discoloring the thermo-sensitive face will not be performedduring the next turn of the optical disk D.

[0092] When stopping the irradiation of the laser beam for the formationof the visible image, the control unit 16 instructs the motor controller32 to move the optical pickup 10 by a predetermined amount to the outerside in the radial direction (step Sa14). The motor controller 32follows the instruction and drives the stepping motor 30 through themotor driver 31 to move the optical pickup 10 to the outer side by thepredetermined amount.

[0093] The predetermined amount by which the optical pickup 10 is movedin the radial direction of the optical disk D may be determined properlyaccording to the spot diameter BS (see FIG. 16) of the beam irradiatedfrom the optical pickup 10. In other words, when the visible image isformed on the thermo-sensitive face of the disk-shaped optical disk D,the irradiation position of the laser beam from the optical pickup 10 ismoved with almost no space on the face of the optical disk D. Such aminute movement is required to realize image formation with higherquality. Therefore, if the unit amount of travel of the optical pickup10 in the radial direction is set to almost the same length as the beamspot diameter BS of the laser beam irradiated on the optical disk D, thelaser beam can be irradiated with almost no space on the face of theoptical disk D. This makes possible image formation with higher quality.However, there is a case that an area larger than the spot diameter ofthe irradiated beam is discolored due to various reasons such as theproperties of the thermo-sensitive face. In such a case, the width ofthe unit amount of travel may be determined by allowing for the width ofthe discolored area so that adjacent discolored areas will not beoverlapped. In the embodiment, since the beam spot diameter BS is setlarger than that at the time of recording on the recording face (forexample, about 20 μm), the control unit 16 controls the motor controller32 to drive the stepping motor 30 to move the optical pickup 10 in theradial direction by a length almost equal to the beam spot diameter BS.Recent stepping motors 30 can employ μ-step technology to control theamount of travel in 10-μm blocks. The use of such a stepping motor 30can be enough to realize the travel of the optical pickup 10 in theradial direction in 20-μm blocks.

[0094] After completion of the control operation for moving the opticalpickup 10 in the radial direction by the predetermined amount, thecontrol unit 16 gives the laser power control circuit 20 a target valuefor write level changed for irradiating laser beam at the write level(step Sa15). In the embodiment, since the CAV method for irradiating thelaser beam while rotating the optical disk D with keeping the angularspeed constant is employed as the method for forming the visible image,when the pickup 10 is moved to the outer side, the linear speed becomeshigh. Therefore, when the optical pickup 10 is moved in the radialdirection (to the outer side), the target value for write level ischanged to be larger than that at that time. In this case, even if thelinear speed is changed due to the change of the target value, laserpower of intensity enough to discolor the thermo-sensitive face of theoptical disk D can be irradiated.

[0095] After execution of the control for moving the optical pickup 10in the radial direction and the control for changing the target valuefor write level, the control unit 16 determines whether there isunprocessed image data for the formation of the visible image, that is,the image data that has not been supplied to the driving pulse generator35 yet. If there is no such image data, the processing is ended.

[0096] On the other hand, if there is unprocessed image data that hasnot been supplied to the FIFO memory 34 yet, the procedure returns tostep Sa7, and the image formation processing is continued. In otherwords, the control unit 16 transfers the image data to the FIFO memory34 (step Sa8), and determines whether the irradiation position of thelaser beam has passed the reference position of the optical disk D (stepSa9). Then, if it has passed the reference position, the control unit 16increments the variable R indicating the number of rotations by one(step Sa10), and determines whether the incremented variable R is an oddnumber (step Sa11). If R is an odd number, the control unit 16 controlseach part of the device so that the laser beam for forming the visibleimage is irradiated in the manner mentioned above. On the other hand, ifR is an even number, the control unit 16 stops the irradiation of thelaser beam for forming the visible image (irradiates the laser beam ofthe servo level). After that, the control unit 16 performs the controlfor moving the optical pickup 10 in the radial direction and the controlfor changing the target value for write level. In other words, whenirradiating the optical disk D with the laser beam for image formation(including the irradiation at the write level) in a certain rotationcycle, the control unit 16 controls not to irradiate the laser beam forimage formation in the next rotation cycle, and performs the control formoving the optical pickup 10 in the radial direction in that rotationcycle. The control for moving the optical pickup 10 and the control forchanging the target value for write level are executed in that rotationcycle, during which image formation is not performed. As a result, anyimage cannot be formed while the irradiation position and the powervalue of the laser beam to be irradiated are varying in the progress ofthe control processing, and the irradiation of the laser beam for imageformation can be performed after the irradiation position and intensityof the laser beam are stabilized. This can prevent a reduction in thequality of the visible image formed with the control operation such asto move the optical pickup 10 in the radial direction.

[0097] The above describes the main operation of the optical diskrecording/reproducing apparatus 100 according to the embodiment. Theoptical disk recording/reproducing apparatus 100 can use each part ofthe device such as the optical pickup 10 for performing informationrecording on the recording face to the fullest extent to irradiate laserbeam on the thermo-sensitive face formed on the optical disk D and forma visible image corresponding to image data without the need to mountadditional printing means.

[0098] Further, in the embodiment, since the irradiation timing of laserbeam is controlled based on a clock signal generated from the FG pulsesgenerated according to the rotation of the spindle motor 11, that is, aclock signal generated according to the amount of rotation of theoptical disk D, the irradiation position of the laser beam can begrasped in the optical disk recording/reproducing apparatus 100 withoutthe need to acquire position information or the like from the side ofthe optical disk D. Therefore, such a limitation that an optical disk Dspecially processed such as that with a pregroove (guide groove) formedon the thermo-sensitive face has to be used is not imposed on theoptical disk recording/reproducing apparatus 100. It allows the opticaldisk recording/reproducing apparatus 100 to form a visible imagecorresponding to image data even on the thermo-sensitive face on which agroove or position information is not preformed.

[0099] When laser beam is irradiated on the thermo-sensitive face of theoptical disk D, since the thermo-sensitive face has low reflectivity, itis difficult to use feedback control based on return light as focuscontrol. If focus control is performed through the application of apredetermined fixed offset voltage or the like to the focus actuator 64,the distance between the optical pickup 10 and the thermo-sensitive faceof the optical disk D will vary due to unevenness on the optical disk Dor rotational variations to disable accurate focus control. On the otherhand, the embodiment performs open-loop focus control according to thepattern of focus control determined based on return light obtained byirradiating laser beam to high-reflective areas (area Da and area Db)beforehand. This makes it possible to perform accurate focus controleven when laser beam is irradiated to a low-reflective area such as thethermo-sensitive face.

[0100] The distance between the optical pickup 10 and the optical disk Dcan vary due to rotational variations or the like on the outer side moreoften than on the inner side. In such a case, the degree of variationsin the distance between both is also made different between the innerside and the outer side. When the focus control is performed based onthe process pattern of focus control obtained by irradiating laser beamto only the inner area Da or the outer area Db, if the distance betweenboth varies widely between the inner radius and the outer radius, theaccuracy of the focus control may be reduced. In contrast, theembodiment uses the process pattern of focus control derived from thecontents of the operations of focus control carried out by irradiatinglaser beam to the inner area Da and the outer area Db, respectively.Further, the embodiment changes the amount of reflection of bothaccording to the irradiation position of the laser beam to decide thefinal focus control contents, thereby performing more accurate focuscontrol.

[0101] C. Modifications

[0102] The present invention is not limited to the aforementionedembodiment, and various modifications are possible as illustrated below.

[0103] (First Modification)

[0104] In the aforementioned embodiment, test laser beam is irradiatedto both the inner area Da and the outer area Db, and based on theprocess pattern of focus control performed during the irradiation of thetest laser beam to both areas, the process pattern of focus controlperformed when laser beam is irradiated to the thermo-sensitive face isdetermined. Alternatively, the process pattern of focus control may bedetermined based on the contents of the focus control performed usingthe return light obtained by irradiating the laser beam to only eitherthe inner area Da or the outer area Db. In the aforementionedembodiment, the inner area Da and the outer area Db, both having highreflectivity, are formed on the thermo-sensitive face of the opticaldisk D. However, if either of the areas has high reflectivity, the laserbeam may be irradiated to only the high-reflective area.

[0105] Further, in the aforementioned embodiment, the inner area Da andthe outer area Db having high reflectivity are targeted. However, thetarget area is not limited to the inner or outer area, and any otherarea may be targeted for the test irradiation of laser beam as long asit is highly reflective enough to obtain return light necessary foraccurate focus control.

[0106] (Second Modification)

[0107] Furthermore, in the aforementioned embodiment, the focus controlas described above is performed as the focus control performed whenlaser beam is irradiated to form a visible image on the thermo-sensitiveface opposite the recording face of the optical disk D. However, thesame control as in the embodiment can be employed as focus controlperformed in any other case, for example, when laser beam is irradiatedon a label face to read a visible image formed on the other side of therecording face (that is, on the label face). Like the above-mentionedthermo-sensitive face, the label face on which a visible image such ascharacters or a picture of a music title or the like is depicted canoften have reflectivity lower than the recording face. Therefore, theuse of the same focus control as that in the aforementioned embodimentwhen laser beam is irradiated on the label face to read the visibleimage can make the focus control more accurate.

[0108]FIG. 19 shows the structure of an optical diskrecording/reproducing apparatus capable of reading a visible image drawnin a low-reflective area such as the label face. As shown, the opticaldisk recording/reproducing apparatus 100′ includes visible imagedetermining part 500 in addition to those of the optical diskrecording/reproducing apparatus 100. In this structure, when reading avisible image such as character information or two-dimensional barcodeformed on the label face opposite the recording face of the optical diskD, the control unit 16 controls each part of the device such as theoptical pickup 10, the servo circuit 13, and the laser power controlcircuit 20 to irradiate laser beam on the label face in the same mannerwhen reading normal EFM data recorded on the recording face of theoptical disk D, except how to perform focus control. Before theirradiation of the laser beam for such reading operation, testirradiation to a high-reflective area (for example, the innermost area)is performed in the same manner as in the aforementioned embodiment.Then, from the contents of the focus control performed in the testirradiation, the process pattern of focus control to be performed whenthe laser beam is irradiated on the label face is determined, and thefocus control is performed according to the determined focus controlcontents.

[0109] In the optical disk recording/reproducing apparatus 100′, thereturn light of the laser beam irradiated on the label face in themanner mentioned above is supplied to the visible image determining part500 through the RF amplifier 12. The visible image determining part 500determines whether the level of a signal supplied from the RF amplifier12 equals or exceeds a predetermined level value, and outputs thedetermination result to the control unit 16. The control unit 16determines the level of contrast or tone in an area of the label face ona coordinate basis. This determination is made based on thedetermination result supplied one by one from the visible imagedetermining part 500, and the position of the laser beam irradiated wheneach determination result is obtained (that is, the radial position andthe angle of rotation from the reference position). Thus the controlunit 16 reads the information such as characters drawn on the labelface. Even when the amount of reflected light from the label face isrelatively small, the above-mentioned determination as to whether thelevel value of the reflected light exceeds the predetermined value makesit possible to determine whether the area is light (e.g., white area) ordark (e.g., black area). Thus, simple characters, a picture, a barcode,or the like can be read out.

[0110] (Third Modification)

[0111] Furthermore, in the aforementioned embodiment, the focus controlis performed based on the return light received by the light-receivingelement 56 having four areas 56 a, 56 b, 56 c, and 56 d. However, whentracking control using a three-beam method is performed, alight-receiving element having two more light-receiving areas inaddition to the four light-receiving areas is used. In an optical diskrecording/reproducing apparatus having such a light-receiving element,focus control may be performed based on the return light received by thelight-receiving element having the six light-receiving areas to decidethe contents of the focus control.

[0112] (Fourth Modification)

[0113] It is assumed inn the aforementioned embodiment that the opticaldisk D is a CD-R, and the description is made of the application of thepresent invention to the optical disk recording/reproducing apparatusfor performing recording on and reproduction from the CD-R. However, thepresent invention may also be applied to an optical disk recordingdevice, reproducing device, recording/reproducing device, or the likecapable of data recording on a CD-RW disk, VD-RW disk, DVD-RAM disk, orthe like.

[0114] (Fifth Modification)

[0115] Furthermore, in the aforementioned embodiment, the control unit16 runs the program stored in the ROM to execute processing includingthe processing for deciding the process pattern of focus control (stepSa7 in FIG. 9). Alternatively, a special-purpose hardware circuit may beso constructed that the processing will be executed by the hardwarecircuit. On the other hand, when the processing is executed viasoftware, a program for letting a computer realize the processing may beprovided to users in the form of various recording media, such as CD-ROMor floppy disk, or provided to users through a communication networksuch as the Internet.

[0116] As described above, according to the present invention, even whena laser beam is irradiated to an area from which a sufficient amount ofreflected light cannot be obtained, accurate focus control can beperformed.

What is claimed is:
 1. An optical disk apparatus for writing or readinginformation by irradiating a laser beam onto an optical disk whilerotating the optical disk under a focus control of the laser beamrelative to the rotated optical disk, the apparatus comprising: anirradiating section that irradiates a laser beam onto the optical disk;a determining section that determines a process pattern of the focuscontrol by operating the irradiating section to irradiate the laser beamonto a predetermined area of the optical disk and by monitoring thelaser beam reflected back from the predetermined area; and a focusingsection that performs the focus control to regulate a spot diameter ofthe laser beam based on the determined process pattern during either ofthe writing or reading of information.
 2. The optical disk apparatusaccording to claim 1, wherein the determining section operates theirradiating section to irradiate the laser beam along a predeterminedround area during at least one turn of the optical disk, and monitorsthe laser beam reflected back from the predetermined round area so as todetermine one round process pattern of the focus control in function ofan angular position of the rotated optical disk, and wherein thefocusing section performs the focus control based on the determined oneround process pattern in response to the angular position of the rotatedoptical disk.
 3. The optical disk apparatus according to claim 2,wherein the determining section determines a process pattern of thefocus control based on a first round process pattern obtained from thelaser beam reflected back from an innermost round area of the opticaldisk and a second round process pattern obtained from the laser beamreflected back from an outermost round area of the optical disk.
 4. Theoptical disk apparatus according to claim 3, wherein the determiningsection determines the process pattern of the focus control byinterpolating the first round process pattern and the second roundprocess pattern in terms of a radial position of the laser beam, andwherein the focusing section performs the focus control based on thedetermined process pattern in response to the radial position of thelaser beam.
 5. The optical disk apparatus according to claim 1, furthercomprising a mount section that can rotatably mount an optical diskhaving a recording face writeable with data information and athermo-sensitive face opposite to the recording face and writeable withimage information, and an image forming section operative when theoptical disk is mounted to expose the thermo-sensitive face foroperating the irradiating section to irradiate the laser beam onto thethermo-sensitive face to thereby form the image information, wherein thedetermining section determines the process pattern of the focus controlsuch that the spot diameter of the laser beam irradiated onto thethermo-sensitive face is regulated greater than the spot diameter of thelaser beam irradiated onto the recording face.
 6. The optical diskapparatus according to claim 5, further comprising a reading sectionthat operates the irradiating section to irradiate the laser beam ontothe thermo-sensitive face of the optical disk to read therefrom theimage information.
 7. A method of focus control of a laser beam relativeto an optical disk rotated in an optical disk apparatus for writing orreading information by irradiation of the laser beam onto the rotatedoptical disk, the method comprising the steps of: provisionallyirradiating the laser beam onto a predetermined area of the opticaldisk; monitoring the laser beam reflected back from the predeterminedarea to detect a variation of a spot diameter of the laser beam;determining a process pattern of the focus control based on the detectedvariation of the spot diameter; conducting the irradiation of the laserbeam onto the rotated optical disk for writing or reading information;and performing the focus control to regulate a spot diameter of thelaser beam based on the determined process pattern during conducting theirradiation of the laser beam.
 8. The method according to claim 7,wherein the determining step irradiates the laser beam along apredetermined round area during at least one turn of the optical disk,and monitors the laser beam reflected back from the predetermined roundarea so as to determine one round process pattern of the focus controlin function of an angular position of the rotated optical disk, and theperforming step performs the focus control based on the determined oneround process pattern in response to the angular position of the rotatedoptical disk.
 9. The method according to claim 8, wherein thedetermining step determines a process pattern of the focus control basedon a first round process pattern obtained from the laser beam reflectedback from an innermost round area of the optical disk and a second roundprocess pattern obtained from the laser beam reflected back from anoutermost round area of the optical disk.
 10. The method according toclaim 9, wherein the determining step determines the process pattern ofthe focus control by interpolating the first round process pattern andthe second round process pattern in terms of a radial position of thelaser beam, and wherein the performing step performs the focus controlbased on the determined process pattern in response to the radialposition of the laser beam.
 11. The method according to claim 7, furthercomprising the steps of rotatably mounting an optical disk having arecording face writeable with data information and a thermo-sensitiveface opposite to the recording face and writeable with imageinformation, and irradiating the laser beam onto the thermo-sensitiveface to thereby form the image information when the optical disk ismounted to expose the thermo-sensitive face, wherein the determiningstep determines the process pattern of the focus control such that thespot diameter of the laser beam irradiated onto the thermo-sensitiveface is regulated greater than the spot diameter of the laser beamirradiated onto the recording face.
 12. The method according to claim11, further comprising the step of irradiating the laser beam onto thethermo-sensitive face of the optical disk to read therefrom the imageinformation.
 13. A program for use in an optical disk apparatus having aprocessor for writing or reading information by irradiation of a laserbeam onto an optical disk while rotating the optical disk under a focuscontrol of the laser beam relative to the rotated optical disk, theprogram being executable by the processor for causing the optical diskapparatus to perform a focus control process comprising the steps of:provisionally irradiating the laser beam onto a predetermined area ofthe optical disk; monitoring the laser beam reflected back from thepredetermined area to detect a variation of a spot diameter of the laserbeam; determining a process pattern of the focus control based on thedetected variation of the spot diameter; conducting the irradiation ofthe laser beam onto the rotated optical disk for writing or readinginformation; and performing the focus control to regulate a spotdiameter of the laser beam based on the determined process patternduring conducting the irradiation of the laser beam.
 14. The programaccording to claim 13, wherein the determining step irradiates the laserbeam along a predetermined round area during at least one turn of theoptical disk, and monitors the laser beam reflected back from thepredetermined round area so as to determine one round process pattern ofthe focus control in function of an angular position of the rotatedoptical disk, and the performing step performs the focus control basedon the determined one round process pattern in response to the angularposition of the rotated optical disk.
 15. The program according to claim14, wherein the determining step determines a process pattern of thefocus control based on a first round process pattern obtained from thelaser beam reflected back from an innermost round area of the opticaldisk and a second round process pattern obtained from the laser beamreflected back from an outermost round area of the optical disk.
 16. Theprogram according to claim 15, wherein the determining step determinesthe process pattern of the focus control by interpolating the firstround process pattern and the second round process pattern in terms of aradial position of the laser beam, and wherein the performing stepperforms the focus control based on the determined process pattern inresponse to the radial position of the laser beam.
 17. The programaccording to claim 13, wherein the optical disk apparatus rotatablymounts an optical disk having a recording face writeable with datainformation and a thermo-sensitive face opposite to the recording faceand writeable with image information, wherein the focus control processfurther comprises the step of irradiating the laser beam onto thethermo-sensitive face to thereby form the image information when theoptical disk is mounted to expose the thermo-sensitive face, and whereinthe determining step determines the process pattern of the focus controlsuch that the spot diameter of the laser beam irradiated onto thethermo-sensitive face is regulated greater than the spot diameter of thelaser beam irradiated onto the recording face.
 18. The program accordingto claim 17, wherein the focus control process further comprises thestep of irradiating the laser beam onto the thermo-sensitive face of theoptical disk to read therefrom the image information.
 19. An opticaldisk apparatus for writing or reading information by irradiating a laserbeam onto an optical disk while rotating the optical disk under a focuscontrol of the laser beam relative to the rotated optical disk, theapparatus comprising: irradiating means for irradiating a laser beamonto the optical disk; determining means for determining a processpattern of the focus control by operating the irradiating means toirradiate the laser beam onto a predetermined area of the optical diskand by monitoring the laser beam reflected back from the predeterminedarea; and performing the focus control to regulate a spot diameter ofthe laser beam based on the determined process pattern during either ofthe writing or reading of information.